1. Field of the Invention
The present invention relates generally to a light diffusion device that is used for inspecting bottle bottoms or the like as an example, and is directed more particularly to a light diffusion device of a simple construction that is suitable for applications to inspect for flaws, dirt and/or foreign material in bottle bottoms.
2. Description of the Prior Art
At bottling production lines, it is generally necessary to have a process between the bottle washing machines and bottle fill or loading machines to inspect for flaws, dirt or mixtures of foreign particles inside the bottles, etc. Such inspection has conventionally depended upon human visual inspection in most cases. Such visual inspection of empty bottles causes eye fatigue in the worker when conducted for long hours (which is the normal case). Eye fatigue increases inspection misses while at the same time such visual inspection limits processing capacity to the human capabilities and high speed inspection is not feasible.
Automatic empty bottle inspection machines are proposed utilizing photo electric conversion means which attempt to overcome such visual inspection defects. An example of such conventional empty bottle inspection machines that use such photo electric conversion means will be explained hereunder in reference with FIG. 1 and FIGS. 2A, 2A' as well as FIGS. 2B and 2B'.
On FIG. 1, 1 is a photo electric conversion means such as photo electric conversion element like a CdS or a video camera, by which the inspected range such as bottom 3 of a bottle 2 or the like to be inspected object is photo sensed, so that it senses flaws, dirt or foreign material on the inside of bottle bottom 3 as a contrast of light and delivers an output as an electrical signal. Changes in the electric output are detected by detection means although not shown on the drawings in order to discriminate flaws, dirt or foreign material on the inside of the bottle bottom 3. On FIG. 1, 4 is a light source which is included a parabolic reflector 4.sub.1 and a lamp 4.sub.2 positioned at the focal point of the reflector 4.sub.1 and which is located at the opposite side of the bottle bottom 3 from the photosensing means and in the example on the drawing is located under the bottle bottom 3. Further, a light diffusing means 5 which is formed of a nontransparent or milky white board to equalize the light from the light source 4 is placed between the light source 4 and bottle bottom 3, by which the light from the light source 4 irradiates the bottle bottom 3 as a uniform or homogenous light.
In this case, the flaws and dirt or the size of foreign particle at the bottle bottom 3 that may be detected can be selected by the brightness of the light source 4 or the sensitivity adjustment of the photo electric conversion means 1 to discriminate very small foreign particles or the like. However, the detection precision is naturally influenced by the structure of the inspected area which is the bottle bottom 3.
In other words, on inspected objects such as bottle 2, it is common that outside protuberances are arranged during the manufacturing process including lines such as line 6 which are generally called baffle marks as shown on FIGS. 2A and 2A', or tear drop like projections which are called knurlings 7 as shown on FIGS. 2B and 2B' or lot numbers or characters or the kind though not shown. Therefore, if the detection sensitivity is raised with consideration only to flaw or dirt detection, the above mentioned protrusions of baffle marks 6 or knurlings 7, etc. will also be detected as light contrasts, in other words, discriminated as an abnormality and it becomes impossible to accurately detect only the flaws, dirt or the like. Accordingly, it is necessary to adjust the detection sensitivity of the system to only detect the flaws, dirt or the like as contrasts of light without detecting the light contrast caused by baffle marks or the like which are unrelated to flaws, dirt or the like.
Actually, in case the detection sensitivity is limited as above described, it naturally causes a reduction in the detection sensitivity of flaws, dirt or the like which should be detected. Therefore, in order to circumvent the reduction of the detection sensitivity without detecting the unnecessary knurlings or the like, conventional detection means have included dipping the outer surface of the bottle bottom 3 into a clear fluid in order to reduce the light refraction at the outside surface of the bottle bottom 3, so that the light contrast of the formed knurling or the like on the outer surface of bottle bottom 3 may be reduced.
However, when bottles that are consecutively moving on conveyor belts or the like are to be automatically inspected, it is extremely difficult task to dip each bottle bottom in such fluid as above mentioned.